Advanced portable oxygen concentrator

ABSTRACT

A portable oxygen concentrator designed for medical use with a novel housing and internal component design that reduces noise and vibration while increasing durability. The improved design of the portable oxygen concentrator further facilitates easy maintenance and repair over the life of the equipment.

RELATED APPLICATIONS

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FEDERALLY SPONSORED RESEARCH

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SEQUENCE LISTING

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BACKGROUND OF THE INVENTION

The invention generally relates to oxygen concentrators, and moreparticularly relates to portable medical oxygen concentrators used bypatients as a 24 hour a day source of supplemental oxygen.

Portable oxygen concentrators are becoming an increasingly desirablemode of supplying portable oxygen needs to patients requiring Long TermOxygen Therapy (LTOT). These portable oxygen concentrators are replacingcompressed gas cylinders and liquid oxygen systems, which have been thestandard of care for many years. Replacing cylinders and liquid oxygenwith a portable oxygen concentrator gives a patient the ability totravel onboard aircraft and avoid the requirement to return home torefill a liquid system or exchange empty cylinders. A particularlyuseful class of portable oxygen concentrators is designed to be used 24hours a day, allowing users to move about and to travel for extendedperiods of time without the inconvenience of managing separate oxygensources for home and portable use. These portable oxygen concentratorsare typically in the range of 2 to 20 lbs and produce from 0.3 to 5.0LPM of oxygen. Most of these portable concentrators are based onPressure Swing Adsorption (PSA) or Vacuum Pressure Swing Adsorption(VPSA) designs which feed compressed air to selective-adsorption beds.In a typical oxygen concentrator, the beds utilize a zeolite adsorbentto selectively adsorb nitrogen, resulting in pressurized, oxygen-richproduct gas.

The main elements in a typical portable therapeutic oxygen concentratorare shown in FIG. 1. Air is draw in, and typically filtered, at airinlet 1 before being pressurized by compressor 2 to a pressure of 1.2 to2.5 atmospheres. The pressurized air is directed by a valve arrangementthrough adsorbent beds 3. An exemplary adsorbent bed implementation,used in a concentrator design developed by the inventors, is two columnsfilled with a lithium exchanged zeolite adsorbent in the ratio of about1 gram of adsorbent per 1-5 ml of oxygen produced. The pressurized airis directed through these adsorber vessels or columns in a series ofsteps which constitute a gas separation cycle, often a PSA cycle or somevariation including vacuum instead of, or in conjunction with,compression yielding overall compression ratios of about 1.5:1 to 4.0:1.Although many different arrangements of adsorber vessels and gasseparation cycles are possible, the result is that nitrogen is removedby the adsorbent material, and the resulting oxygen rich gas is routedto a product gas storage device at 4. Some of the oxygen product gas canbe routed back through the bed to flush out (purge) the adsorbednitrogen to an exhaust 6. Generally multiple adsorbent beds, or columnsin the exemplary device, are used so at least one bed may be used tomake product while at least one other bed is being purged, ensuring acontinuous flow of product gas. The purged gas is exhausted from theconcentrator at the exhaust 6.

Such gas separation systems are known in the art, and it is appreciatedthat the gas flow control through the compressor and the adsorbent bedsis complex and requires precise timing and control of parameters such aspressure, flow rate, and temperature to attain the desired oxygenconcentration of 80% to 95% purity in the product gas stream.Accordingly, most modern concentrators also have a programmablecontroller 5, typically a microprocessor, to monitor and control thevarious operating parameters of the gas separation cycle. In particular,the controller controls the timing and operation of the various valvesused to cycle the beds through feed and purge and pressure equalizationsteps which make up the gas separation cycle. Also present in mostportable concentrators is a conserver 7 which acts to ensure that oxygenrich gas is only delivered to a patient during inhalation. Thus, lessproduct gas is delivered than by means of a continuous flow arrangement,thereby allowing for smaller, lighter concentrator designs. A pulse ofoxygen rich air, called a bolus, is delivered in response to a detectedbreath via the conserver. Using a conserver in conjunction with a gasconcentrator may reduce the amount of oxygen required to maintainpatient oxygen saturation by a factor of about 2:1 to 9:1 A typicalconcentrator will also contain a user/data interface 8 includingelements such as an LCD display, alarm LEDs, audible buzzers, andcontrol buttons. In addition to the above subsystems, most portableoxygen concentrators contain a rechargeable battery and charging systemto power the concentrator while away from an AC or DC power source.These battery systems are typically composed of lithium ion cells andcan power the concentrator from 2-12 hours depending on the amount ofoxygen required by the patient and the capacity of the battery pack.

To be practical and usable by a individual needing therapeutic oxygen,portable oxygen concentrators should be less than about 2100 cubicinches and preferably less than 600 cubic inches in total volume, lessthan about 20 pounds and preferably less than 8 pounds in weight, andproduce less than about 45 decibels of audible noise, while retainingthe capacity to produce a flow of product gas adequate to provide for apatient's oxygen needs, usually a flow rate prescribed by a medicalpractitioner in about the range of 1 LPM to 6 LPM. Further, a portablemedical oxygen concentrator must work under varied environmental andphysical conditions without costly or frequent service or maintenancerequirements and should be able to run for upwards of 20,000 hoursbefore major maintenance is required, such as a compressor rebuild.Although fixed site PSA based concentrators have been available for manyyears, such fixed site units may weigh 30-50 pounds or more, be severalcubic feet in size, and produce sound levels greater than 45 dBA. Thusportable concentrators involve a significant amount of miniaturization,leading to smaller, more complex designs compared to stationary units,yet they must remain relatively low cost to be available to a wide rangeof users. System size, weight, and complexity may lead to a necessarilyhigher degree of integration and design optimization. Moreover, the costconstraints of portable concentrators preclude the use of multiplepressure, temperature, and concentration sensors used by large scaleindustrial concentrators to help optimize efficiency. Significantteachings in concentrator art exist on just the subject of monitoringand control of various parts of the PSA process. Yet ultra-smallportable concentrators have as much or greater need to accomplish suchprocess control. A major required area of innovation in portableconcentrator design is the need to accomplish the sort of processcontrol practiced in large scale units without the luxury of the toolsavailable to large scale system designers.

One particular challenge of portable concentrator design is that thedevices are typically carried by the user. Since stationary oxygenconcentrators are left in one site and the user uses a 50 ft tubeextension to move about, the device is not nearly as close to the userunder most circumstances. The portable oxygen concentrator musttherefore be quieter, create less vibration, and be much more resilientto impacts, and function under constant movement and in various physicalorientations.

Therefore, it is necessary to design a portable oxygen concentrator thatincorporates an improved mechanical design that mitigates noise andvibration while simultaneously protects the device during impact. Priorart portable oxygen concentrators fail to meet all of these designcriteria and as a result, the previously available products did not meetall the needs of the users and the home medical equipment providers.These prior art concentrators failed to meet the users' needs by beingtoo large, too loud, and operated with too much vibration to be near theuser 24 hours a day. These prior art concentrators similarly failed theequipment providers due to frequent malfunctions and short servicelives. Some prior art portable oxygen concentrators may need a completecompressor rebuild after only 4000 hours, which equates to roughly sixmonths of 24/7 usage. The portable nature of the equipment exposes thedevices to being dragged over rough roads, bounced around in the trunksof cars, and knocked off counter tops to impact the ground from severalfeet. While some prior art equipment might hold up to these high levelsof abuse, they do so with added weight and reduced performanceparameters such as high noise levels or lowered oxygen flow rates.

Oxygen equipment used for Long Term Oxygen Therapy (LTOT) is optimallydeployed for 3-5 years without any service requirements, but when thereare service requirements or repairs, they must be able to be performedquickly and inexpensively. Prior art portable oxygen concentrators donot meet the objectives of fast and inexpensive repair in the event ofdamage. Many systems utilize adhesives to permanently bond partstogether or have many components integrated into the outer housing suchthat replacing a damaged housing requires a nearly complete rebuild ofthe system. Not only do these assembly methods lead to more expensiverepairs, but they limit the scope of facilities that can perform therepairs due to requirements for specific tooling and fixturing thatcommon repair facilities would not have access to.

BRIEF SUMMARY OF THE INVENTION

The devices, systems, and methods of this invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention, its moreprominent features will now be discussed briefly. In one embodiment, theinvention provides a portable oxygen concentrator that incorporatesnovel mechanical design elements to achieve a low noise, low vibration,durable, and easily repaired design. This integrated design approachenables the portable oxygen concentrator of the preferred embodiments tomeet the needs of patients and equipment providers where prior artdesigns have failed. The novel mechanical design elements include theassembly method of the outer housing components, low volume vibrationisolation of the compressor, overlapping housing baffles, and floatingcolumn clip assembly system.

Even the inventors' most robust mechanical designs may succumb to thecontinued abuse of some users, so the inventors designed a novel outerhousing assembly system that allows for fast and inexpensiverefurbishment of the concentrators so that equipment providers canminimize repair time and cost. In certain preferred embodiments, none ofthe internal functional components of the housing assembly are anchoredto the housing panels, which allows for fast replacement as well asimproved vibration and noise isolation.

In a preferred embodiment the housing of the portable oxygenconcentrator comprises at least four panels that snap fit together toform convoluted sound baffles for noise abatement. The outer housingpanels preferably snap together with retention clips, and some of theseclips may be further secured with fasteners in order to still meet therigorous durability requirements of this class of device.

In one embodiment, at least two of the panels when assembled form aninlet air plenum, and at least two panels form an outlet air plenum. Ina particular aspect, the air plenum is a space between a double-walledsection formed by the assembled panels. In one particular embodiment,the side panels wrap around the front and back of the device to matetogether forming the inner wall of the double-walled structure. The sidepanels further have mirror-imaged cut-outs to form the inner air ventopening at the front of the device and the inner exhaust vent opening atthe rear of the device. To form the outer wall of the intake or exhaustplenum, a convex and stylized end panel is snapped over the mated sidepanels forming a hollow air plenum. The opening in the end panel isoffset from the opening formed in the wall section of the side panelsand air flows through the space formed between the end panels and thewall section of the side panels. The path through both plenums isoffset, preferably substantially non-overlapping or completelynon-overlapping, to provide noise isolation. A mesh screen may be usedon the inlet to keep the airways clear of debris. Between the inlet andoutlet plenums there is at least one air barrier, preferably sealed tothe housing panels, preferably nonridgidly with foam. An air mover,typically a cooling fan or blower, is carried by the air barrier andprovides a forced air path through the barrier. In a preferredembodiment, the air barrier is a printed circuit board. In one as-builtembodiment, the adsorbent bed columns are on the inlet side of the airbarrier and the compressor is on the outlet side.

In another embodiment, a bottom panel includes a battery mount, and thebattery and panels go together such that when the battery is installed,the battery contacts and retains at least two and preferably all of thefront, side and rear panels to improve the rigidity of the assembly. Thebattery is also preferably part of the aesthetic design of the housing.

In another preferred embodiment the adsorbent columns are carried by aplurality of, preferably two, vibration/shock absorbing mountingelements. These mounting elements may be foam blocks with cutouts, suchthat the columns are held by the blocks and do not come into directcontact with the housing. In a particular embodiment, the foam is moldedurethane. Additionally, the concentrator may contain one or more modularclips that locate the adsorbers and other components relative to eachother between the blocks without making any attachments to the housingcomponents.

In a particular embodiment, the modular clips also mount the airbarrier/mover, preferably a circuit board and cooling fan, to form anair dam that allows for unidirectional cooling flow that simultaneouslyintakes room air for the PSA cycle and exhausts waste nitrogen gas fromthe system without recirculation. Other elements that may be mountedwith the columns in the floating assembly include an air dryer, anoxygen product accumulator, and an oxygen sensor.

In a preferred embodiment, the compressor is mounted to a bracket whichis in turn mounted to one or more of the housing panels, preferably anon-exterior housing panel to maintain ease of outer housingreplacement. The compressor is mounted to the bracket withshock/vibration isolating elements, which in one embodiment may beovermolded rubberized mounts. The bracket is preferably mounted to thehousing with a further set of shock/vibration isolating elements,providing two levels of isolation. In one embodiment, the bracketmounting elements are rubberized feet and in a particular version rubberfeet with a durometer of 20 A to 60 A. In one version, the bracket isaluminum. The bracket may additionally mount one or more airflowmanifolds. The bracket and the lower housing may also preferably includebump stops to limit compressor and bracket deflection during drop orimpact.

In one version of the invention, the compressor intake is routed throughthe fan ducting to ensure a supply of fresh air is always drawn into thecompressor.

In another embodiment an inlet air filter attaches to the compressor.The filter preferably has a tortuous air path for noise reduction, andfurther may be mounted with its inlet and outlet at right angles to eachother for further noise reduction. Substantially all air connections toand from the filter/compressor assemble are by compliant airflowcomponents, and in a particular embodiment molded compliant airflowcomponents to ensure minimum force is applied to the compressor when itis located in its nominal position.

In another embodiment the compressor is a two piston unit where thepiston inputs are fluidly connected by a low profile compliant member.The compliant member in one version comprises one snap fit and onethreaded attachment to the pistons. In various versions, the compliantmember may be at least two parts of molded rubber joined together, andthe member cross section is in the range of 0.02 to 0.08 square inches.

In another embodiment, the portable oxygen concentrator includes apressure sensor mount where a compliant bracket mounts the pressuresensor and in turn the bracket is mounted to the circuit card. This hasthe effect of eliminating the hard mounting of the sensor at itsdesigned attachment points, improving the tolerance of the sensor tofalse readings due to vibration.

BRIEF DESCRIPTION OF THE DRAWINGS

The understanding of the following detailed description of certainpreferred embodiments of the invention will be facilitated by referringto the accompanying figures.

FIG. 1 shows the general elements of gas concentrators as applicable tocertain embodiments of the invention.

FIG. 2 shows two views of a novel concentrator according to a preferredembodiment.

FIG. 3 shows an exemplary outer housing panel arrangement incorporatedin the novel concentrator shown in FIG. 2.

FIG. 4 illustrates the panel snap retention clips and fastenersincorporated in the novel concentrator shown in FIG. 2.

FIG. 5 depicts the air path through the concentrator body, air barrier,and blower incorporated in the novel concentrator shown in FIG. 2.

FIG. 6 illustrates the arrangement of the compressor, mounting bracket,air filter and air input member incorporated in the novel concentratorshown in FIG. 2.

FIG. 7 shows a novel pressure sensor mount incorporated in the novelconcentrators shown in FIG. 2.

FIG. 8 depicts the isolation and mounting of the adsorbent columnsincorporated in the novel concentrator of FIG. 2.

FIG. 9 depicts the novel concentrator of FIG. 2 in a substantiallyassembled form.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, general features of a portable therapeutic gasconcentrator are shown. Typically gas is drawn into the inlet through aninlet filter 1 into a compressor 2. Compressed air is then delivered ata rate of about 3 LPM to 30 LPM (through various filters and otherdevices) to a gas separation section for selectively adsorbing acomponent of the gas. The preferred embodiments of the invention,although applicable to a variety of gas concentrator implementations,will be described in detail for the case where the inlet gas is air, andthe gas separation section is based on PSA, VSA, VPSA or somecombination thereof, utilizing adsorbent beds 3 which selectively adsorbnitrogen, producing oxygen rich product.

A variety of gas separation section cycle types and bed arrangements areknown in the art, most of which can benefit from the embodiments of theinvention. Whatever the details of the gas separation section 3,typically product gas is accumulated in a storage device 4. Storagedevices may include a tank in the traditional sense, or may be someother device effective for holding a volume of gas, such as a tube, orsome other volume filled with an adsorbent to increase its holdingcapacity. Many modern concentrators used for therapeutic applicationsalso include a programmable controller 5 to operate the concentrator andprovide for user interface 8 and communications. Also typical are gasexhaust 6, and delivery to patient, which often is through a conserverdevice 7.

Earlier portable oxygen concentrator designs were heavier and typicallyhad an oxygen output of only around 0.1 L/lb of system weight. This lowoutput to weight ratio was largely a result of thicker housing walls andredundant components to aid in sound reduction and vibration isolation.For a system that can be carried by the user by a shoulder strap orbackpack system, a higher oxygen output to weight ratio is desired.Embodiments of the current invention increase the oxygen to weight ratioby as much as 30% over prior art concentrators while also achievinglower sound levels and increased durability. By comparison, popularexisting systems have muck lower oxygen to weight ratios. The Inogen Onedelivered 0.75 L of oxygen and weighed 9.7 pounds for an output toweight ratio of 0.08 L/lb. The Respironics Everglo in measurements madeby the inventors produced 1.05 L of oxygen at 10.2 pounds for an outputto weight ratio of 0.10 L/lb. The inventors also tested the AirSepFreeStyle and measured 0.45 L of oxygen and weighs 4.3 pounds for anoutput to weight ratio of 0.10 L/lb. While efforts have been made toachieve greater oxygen output to weight ratios in transportable unitssuch as continuous flow portable concentrators like the SeQual Eclipse,these units have integrated cart handles and wheels so they are notdesigned for the same purpose as a carried or worn concentrator and arenot as likely to experience the same level of abuse as the type ofconcentrator designed by the inventors. As a portable concentratorshrinks to a size where it can be carried, the likelihood of significantdrop and impact is greatly increased, while the requirement forcomponent and system weight reduction is also greatly increased. Systemhousing wall thickness may be reduced from 0.050″ down to 0.030″ or lessdepending on the flame rating requirements of the selected material.Further, as the volume of the concentrator shrinks from around 1200cubic inches to less than 500 cubic inches or even 300 cubic inches, thenoise, vibration, and heat generating components become ever closer tothe housing walls, and inlet vents, and exhaust vents. This volumereduction necessitates improved functionality from noise mitigation andvibration mitigation designs while not allowing for additional size orweight to achieve the noise and vibration reductions. For instance theinventors tested the Invacare XPO2 and measured a high oxygen to weightratio of 0.12 L/lb producing 0.84 L of oxygen at 7.3 pounds, butobserved noise level increases to above 45 dBA as a result. Asminiaturization of a portable oxygen concentrator progresses thedesigners are faced with ever more difficult challenges, and thisdisclosure details several novel design approaches that offer solutionsto weight, noise, and durability requirements.

The Figures depict exemplary implementations that resemble portions ofan as-built novel concentrator. However it is to be understood that thedetails in the Figures are by way of example only and in many casesserve to illustrate a particular version of a novel concept that neednot follow the exact configuration of the figures to fall within theteachings and claims of the invention. Referring to FIG. 2 a generalillustration of the novel concentrator is shown. Concentrator housing21, battery 22 and user interface 8 are shown. The battery 22, asdepicted in the exemplary figure, forms a nearly seamless integrationwith the concentrator so that the battery actually forms the bottom ofthe concentrator and has integral overmolding that functions as animpact absorber and anti-slip footing for the concentrator. Since manydrops and impacts would be taken by the bottom of the concentrator, thelocation of the battery provides a level of protection where damage tothe battery would not stop the concentrator from functioning on externalpower such as AC or DC power. In addition, the sliding rails of thebattery and the interlocking components that form the mating rail on theconcentrator form a particularly strong and rigid area of theconcentrator that allow the battery and shell of the concentrator todissipate energy without harmfully transmitting it to the workinginternals of the device. The housing 21 of the concentrator is alsodevoid of corners and flat surfaces to further stiffen the outer shell,which allows for reduced wall thickness without reduced durability.

FIGS. 3 a and 3 b depict a particular embodiment of the concentrator 21.Base panel 33 connects to side panels 31 and 32 as well as front panel34 and rear panel 35 as can be seen when front and rear panels 34 and 35are attached they form an air plenum with an offset flow path, which forthe exemplary panel design shown is completely non-overlapping. Thisoffset ducting design is a significant improvement for noise isolation.A mesh screen 37 may be employed as a debris filter on the input airplenum. At least some and preferably all the side, front and rear panelsare configured to overlap bottom panel 33. When battery 22 is installed,it is configured to contact and retain the panels for added rigidity.Similarly top panel 35 also contacts all of the body panels as well. Inthe exemplary implementation, the air plenum space formed by the matingof panels 31, 32, and 34 and the similar air plenum space formed by themating of panels 31, 32, and 35 create a double-walled structure wherethere are a plurality of connecting points, preferably eight or more.These double walled structures are similar in function to the batteryattachment on the bottom of the concentrator where multiple componentsare mated to increase rigidity and strength while also providing fornoise reduction and easy serviceability. In one particular embodiment,the side panels wrap around the front and back of the device to matetogether forming the inner wall of the double-walled structure and arethe two side panels and the top panel are joined with a single screwcreating a three-point anchor system. The side panels further havemirror-imaged cut-outs to form the inner air vent opening at the frontof the device and the inner exhaust vent opening at the rear of thedevice. To form the outer wall of the intake or exhaust plenum, a convexand stylized panel is installed by engaging retention clips thatprotrude from the convex outer panel through slots in the side panels.These clips and slots are locked into place when the panel is slidupward and further reinforced because the battery blocks the panel fromdisengagement in the downward direction. The opening in the end panel isoffset from the opening formed in the wall section of the side panelsand air flows through the space formed between the end panels and thewall section of the side panels. The path through both plenums isoffset, preferably substantially non-overlapping or completelynon-overlapping, to provide noise isolation by eliminating a direct pathfor noise to exit the device.

As shown in FIGS. 4 a, b, and c panels can be attached to each other viaan interference fit such as snapped together with retention clips 42 and43. When assembled, retention clips may be further reinforced withfastener mounts to ensure that housing holds its shape during impact toprevent undue deformation to internal components. The multitude ofsnapping features or other forms of interference fit type of fasteningdevices also allows for a reduction in the number of screws or fastenersrequired to assemble the concentrator since panels can be locked inplace by two fasteners while maintaining strength around the entireperimeter of the panel through the snap features. This assembly methodgreatly reduces the assembly time and weight that would be required tohave a high number of fasteners. For example, the SeQual Eclipse is asimple clamshell design that uses 10 screws to fasten the two halvestogether. The inventors design uses 13 screws to fasten six panelstogether for roughly 50% less fasteners per housing panel. A particularimplementation is shown in FIGS. 4 b and 4 c. As shown in FIG. 4 b, whenside panel 31 is mated with bottom panel 33, a rail is formed along thelength of the panels. When battery 22 is installed, the side panel canno longer be removed because the retention clips must be disengaged inthe direction of movement that is blocked by the battery 22. As shown inFIG. 4 c, back panel 35 attached to side panels 31 and 32 by slidingupwards to engage the retention clips 43. When battery is installed,back panel 35 is prevented from sliding downward and thus cannot bedisengaged by drop or impact. Similar arrangements as shown in theFigures also apply to the front and other side panels. Thus when battery22 is installed, all four panels are contacted and restrained such thatthe panels cannot be disassembled with battery in place and structuralintegrity is greatly increased. Referring to FIG. 5, the plenums formedby the assembled panels are shown. Input 52 is offset from opening 53 asoutput 55 is offset from opening 54. Preferably an air barrier 50 ispresent within the housing between the input and output plenums, and itcarries an air mover 51, which provides the only airflow path throughthe barrier. In a particular embodiment barrier 50 has a plurality offunctions such as an electronic circuit board and air mover 51 is acooling fan mounted to the board 50. The circuit board 50 is preferablysealed to the housing with foam to prevent air leakage back across theair barrier. The air flow through the body is as shown. In a particularas built embodiment, the adsorber columns are in the input side of thebarrier and the compressor is in the output side of the barrier. Whenassembled the panels and barrier constitute a very rigid shell withcontrolled low noise airflow that is particularly suited to an oxygenconcentrator where room air must be drawn into the system as a source ofoxygen and the nitrogen rich exhaust gas must be expelled from theconcentrator. It is advantageous to separate these gas streams so thatthere is no excess nitrogen drawn into the air inlet of the compressor.

Referring to FIGS. 6 a, b and c, details of the compressor side of thenovel concentrator are shown. In the exemplary version depicted, acompressor bracket 64 is mounted to panel 33. Bracket 64 is preferablymounted to panel 33 with shock/vibration isolating elements which in theexemplary version shown are rubber feet 65. Feet 65 preferably have adurometer between 20 A and 60 A. Compressor 62 is in turn mounted tobracket 64 with another set of shock/vibration isolation elements,providing two levels of isolation. In the exemplary version, the secondset of isolators is fabricated on the bracket as overmolded rubber 64.Panel 33 in an as-built configuration is the only housing panel withstructural mounting for a vibrating component. Panel 33 is an internalpanel where the battery is mounted on the underside of the panel. Thispanel is particularly suited for compressor mounting since the highlymass dense battery absorbs much of the transmitted vibration andprevents the transmission of vibration to the side panels that maycontact the user while the device is being carried. In the inventors'prior art concentrator the compressor was mounted to a separate internalchassis that was then surrounded by housing components which led toadded weight and size. The separate internal chassis of the prior artconcentrator was also more susceptible to damage during drop or impactbecause the structure was not supported across much of its surface area.Panel 33 is fully supported by battery 22 leading to a much stronger andmore resilient design.

Bracket 64 may be made of aluminum for example and in the exemplaryversion the compressor 62 is a two piston unit. The two piston inputsare connected by low profile compliant member 63. Element 63 in theembodiment shown is a rubber duct 630 and 631 with one snap fit and onethreaded attachment to allow for vertical compliance since thecompressor assemblies are pressed onto the motor shaft without a hardstop to prevent bearing loading. It may be made from two joined moldedrubber pieces and the air channel preferably is between 0.02 and 0.08 sqin. The compliant member preferably has a durometer between 20 A and 70A to prevent the flat surfaces from resonating noise. The inventorstried multiple materials and fabrication methods and achievedunacceptable results until the proper material and durometer wereselected. The flat geometry of the compliant member allows for adequatecross section to prevent flow loss from the compressor while alsominimizing the protrusion height from the concentrator. With the smallexternal dimensions of a carried portable oxygen concentrator allcomponents must be optimized to reduce space in critical directions.Prior art intake joining tubes were two hard plastic cylinders that slidinternal to one another for compliance and protruded as much as twice asfar from the compressor as the inventors compliant member 63.

Air filter 61 is preferably arranged with its input and output at rightangles and has a tortuous air path 610 again for noise isolation. Airfilter 61 is plumbed to the air blower with compliant tubing in thedurometer range of 20 A to 60 A. The compressor mounting arrangementpreferably also includes bump stops 66 to limit compressor deflection inthe event of the concentrator being dropped or impacted. Stops 66 areplaced adjacent to mounting feet 65 and compressor 62. The stops 66built into bracket 64 substantially prevent the compressor fromcolliding with delicate components like the printed circuit board or theexternal housing components. The bump stops 66 adjacent the mountingfeet 65 also allow for softer mounting feet to be used without risk oftearing due to over deflection during drop or impact. Bracket 64 mayalso include mounting for beds with compliant airflow elements.

When assembled, the compressor filter assembly is mounted to the housingthrough two layers of isolation and only connected to the rest of thesystem through compliant elements. Thus the assembly is highly resistantto shock and displacement while providing vibration and noise isolation.

FIGS. 7 a and 7 b illustrate another embodiment of the novelconcentrator. Pressure sensor 72 is designed to mount to a circuit card50 with two fasteners. This in effect is a stiff fixed mounting that cancreate a torque or twist on the sensor between the mounting screws andthe barbed tubing connections. Due to the shock, vibration and generalmotion experienced in the portable concentrator environment, this fixedmounting point induced strain can couple vibration into the sensor andcan affect the quality of the measured reading. The inventors developedclip 73 which snap mounts to the sensor 72 and is a cantilever designedto mount into the fastener points intended for the sensor, whilesuspending the sensor itself so that it is mounted near the barbedtubing connections to relieve any strain air manifolds which again arepreferably plumbed to the adsorber or stress on the body of the sensorwhere the delicate pressure measuring components are housed. This strainrelief in effect greatly diminishes the vibration coupled into thesensor and allows for more reliable and more sensitive breath detectioncapabilities.

Referring to FIG. 8, the adsorber bed side of the concentrator of oneembodiment is detailed. Adsorber columns 81 are supported, preferably atthe top and bottom by isolation elements which fit into the housingpanels such as panel 33. These elements are in the exemplary versionshown, foam blocks 82 and 83 with cutouts supporting the columns. Thecolumns are located and held relative to each other by clips 84. Clips84 and blocks 82 and 83 may also carry one or more other items inaddition to adsorber beds, including air dryers, an oxygen sensor, andproduct gas accumulator. Thus the columns and other items are floatingin the housing with no hard contact to the housing at all. Thisarrangement greatly improves the durability and survivability of theconcentrator while providing yet more noise and vibration isolation.Further in some embodiments, the columns are held in the concentratorwithout any screws whatsoever allowing for very simple columnreplacement if the zeolite is ever contaminated.

In addition, noise barrier 50 and blower 51 may also be mounted in thefoam blocks. The resulting assembly shown in FIG. 9 illustrates theoverall concentrator assembly of one embodiment. Rigid and strong shell21 composed of interlocking panels and locked by battery 22 has nodirect contact with any interior components. The columns 81, dryer,accumulator and all electronics 50 and fan 51 float in a foam chassis 82and 83 on one side of the air barrier. Compressor 62 vibrates too muchto use a foam chassis, so it and all directly attached components aresupported by two levels of rubberized isolation, again with no directhard attachment to the exterior housing panels. In one implementation,the only communication between the two sections is by way of compliantairflow elements such as soft plastic tubing and the like. Airflow iscarefully designed to reduce noise. The result is a very hard shell,with all interior components possessing a large amount of freedom ofmotion relative to the shell and each other, producing an extremelydamage resistant and very quiet design.

The foregoing description of the preferred embodiments of the presentinvention has shown, described and pointed out the fundamental novelfeatures of the invention. It will be understood that various omissions,substitutions, and changes in the form of the detail of the apparatus asillustrated as well as the uses thereof, may be made by those skilled inthe art, without departing from the spirit of the invention.Consequently, the scope of the invention should not be limited to theforegoing discussions, but should be defined by appended claims.

We claim:
 1. A portable oxygen concentrator, comprising: An outerhousing comprising; removable panels including at least two of thefront, back, side and top panels; and, at least one of the air intakeand exhaust path in the panels disposed wherein an air path follows anoffset path through at least two panels at the air intake and two panelsat the air exhaust of housing; wherein the concentrator weighs less than8 pounds, produces less than 45 dba acoustic noise when operating, andhas an output gas flow of less than 5 lpm and has an externally mountedrechargeable battery capable of running the concentrator for greaterthan 2 hours.
 2. The outer housing of claim 1 wherein the panels areattached together by interlocking retention units.
 3. The outer housingof claim 2 wherein the interlocking retention units are locked in placewith fasteners.
 4. The outer housing of claim 1 further comprising abattery mount wherein a battery unit installed in the mount contacts atleast two of the front, side, bottom and back panels to increase therigidity of the housing.
 5. The outer housing of claim 1 where a batteryforms a portion of the aesthetic exterior of the concentrator.
 6. Theoxygen concentrator of claim 1 further comprising at least one barrierelement between the intake and exhaust portions of the housing, whereinthe barrier element contains an air mover disposed wherein air flow fromthe intake to exhaust is through the air mover.
 7. The oxygenconcentrator of claim 6 wherein absorber column beds are on the inletside of the barrier element and an air compressor is on the air outletside of the barrier element.
 8. The concentrator of claim 6 wherein thebarrier element is a printed circuit board.
 9. The concentrator of claim6 wherein the barrier element is sealed non rigidly around its edges tothe outer housing panels with foam.
 10. The concentrator of claim 6wherein the air mover is a cooling fan.
 11. The concentrator in claim 1where an intake vent comprises a mesh screen to prevent contaminantsfrom entering a concentrator.
 12. The concentrator of claim 1 whereoffset openings in the intake or the exhaust are completelynonoverlapping.
 13. The housing panels of claim 1 where retention unitsinterlock at least each panel to every adjacent panel.
 14. A portableoxygen concentrator, comprising: An air intake; An air exhaust; An outerhousing defining an enclosure, wherein the outer housing comprising atleast one double-walled section, said double-walled section comprises anouter wall and an inner wall separated by a space and forming an airflow path through which air passes in its path from the air intake tothe air exhaust; A PSA unit disposed inside the enclosure, said PSA unitcomprising of plural absorbent beds, said unit including valvesoperating in accordance with a PSA cycle; and A compressor disposedinside the enclosure, said compressor is connected to supply compressedair to the PSA unit, said compressor is configured to draw ambient airthrough the air intake.
 15. The portable oxygen concentrator of claim14, wherein the outer housing comprises two end panels and two sidepanels wherein each side panel has a wrap around section at the frontand rear, forming a wall section when mated.
 16. The portable oxygenconcentrator of claim 15, wherein the end panels are removablyattachable to adjacent side panels via an interference fit.
 17. Aportable oxygen concentrator, comprising: An outer housing defining anenclosure, said outer housing having an upper exterior surface, a lowerexterior surface, and side surfaces extending there between; A PSA unitdisposed inside the enclosure, said PSA unit comprising plural absorbentbeds, said unit including valves operating in accordance with a PSAcycle; A compressor disposed inside the enclosure, said compressor isconnected to supply compressed air to the PSA unit; and A battery, saidbattery is mounted on the lower exterior surface of the outer housing,said battery is configured to conform to the contours of the lowerexterior surface so as to serve as a bottom support of the portableoxygen concentrator.